Masses and radii of white-dwarf stars. IV. The two-color diagram

Newly calculated model atmospheres, including both the effects of Lyman and Balmer line blanketing and the effects of convection, are used to determine the surface gravities of white-dwarf stars by the use of the separation of stars with different surface gravities in the Stroemgren and multichannel two-color diagrams. The mean surface gravity of 40 stars in the appropriate temperature range with multichannel colors is log g=8.04 +- 0.25, and the mean value for 35 stars with Stroemgren photomety is log g=7.86 +- 0.25. Comparison of all available investigations of white-dwarf masses shows that they are internally consistent with the possible exception of masses derived from gravitational redshifts, where a slight, marginally significant discrepancy may exist. The weighted mean of all mass determination is 0.75 M/sub sun/, allowing for selection effects. The 1 sigma range of white-dwarf masses extends from 0.5 M/sub sun/ to 1.0 M/sub sun/; we do not find evidence for a smaller mass range